Why does my transaction show up as a recurring charge?
You will not be charged twice for your transaction. It is a single transaction and is not recurring.
You may have noticed on your bank statement that your Structure transaction falls under the "recurring payments" section. We can assure you that your payment is not recurring and that Structure is not currently using recurring payments as a payment method. This happens while placing a pre-order for something that has not been released (or is currently on backorder); your card will only be charged when the item is shipped and will not be charged until then. For this reason, your card information is saved (and highly encrypted) so that the transaction will be completed once the order has shipped.
For processing payments Structure uses Stripe. According to Stripe's Support Pages, the reason the charge shows up as recurring is due to PCI compliance.